I'd wager that if someone is a drinking/drugging buddy, they may have a problem. Maybe not. But if there is a chance they do, then eventually, they will get it, if they ever get sober, and maybe even if they don't. I'd ignore them, or blow them off by saying "sorry, I'm busy." over and over again until they stop calling. If your interactions are solely based in partying, then they will almost completely likely not change. Remember they too have an AV and that AV will be the one talking if they ask you to go out after you tell them you are getting sober. Tough love.
To summarize... what sober wolf said. Eliminate all contact.